Abstract 12267: The Alpha1 Isoform of Soluble Guanylate Cyclase Regulates Cardiac Contractility but is not Required for Cardioprotective Signaling
Background: Soluble guanylate cyclase (sGC) stimulation is an important signaling event in various cardioprotective pathways, with potential clinical applications in cardiac critical care and resuscitation. The sGCα subunit, which binds to the common sGCβ1 subunit, exists in 2 different isoforms, sGCα1 and sGCα2, but their relative physiological roles remain unknown.
Methods: We studied Langendorff-perfused isolated hearts of genetically engineered mice lacking functional sGCα1 (sGCα1KO mice), which is the predominant isoform in the heart. We subjected the hearts to 40 min of global ischemia and 1 hour of reperfusion, with or without ischemic preconditioning (IPC) to elicit cardioprotection.
Results: Deficiency of sGCα1 enhanced both inotropy and lusitropy in isolated hearts, indicating an important role for this isoform in regulating basal myocardial contractility. Surprisingly, cardioprotection by IPC led to a similar reduction in infarct size in both wild-type (WT) and sGCα1KO hearts (from 41 ± 4% to 26 ± 2% in WT and from 40 ± 2% to 24 ± 2 % in sGCα1KO hearts, for both: P<0.01 vs control without IPC; N=6–8 per group). The extent of cardioprotection correlated with the degree of protein kinase Cε (PKCε) phosphorylation. Inhibition of the activation of all sGC isoforms by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) completely abolished the protection by IPC in WT hearts (infarct size: 44 ± 4% without and 41 ± 3% with IPC; N=5 each). PKCε phosphorylation was not increased after IPC in ODQ-treated hearts. Of note, stimulation with a nitric oxide (NO) donor significantly increased the cGMP-release from WT hearts, but not from sGCα1KO hearts or WT hearts treated with ODQ.
Conclusions: These results indicate that although sGCα1 importantly regulates cardiac contractility, it is not required for cardioprotection. Instead, our results suggest that the minor sGCα2 isoform, which does not produce detectable amounts of cGMP after NO stimulation, is required and sufficient to transduce the cardioprotective signal via phosphorylation of PKCε. The development of sGCα2-specific stimulators might have important clinical benefits, especially in light of the negative inotropic and lusitropic effects of sGCα1-derived cGMP that we report in this study.
- © 2010 by American Heart Association, Inc.